IAT question

[odd boy]

what happens to the car idle when the IAT is disconnected? I know air temp plays a major rule in calculating the air density so it will affect a lot of parameters.

I am asking for that piece of info in order to tune a car that will be used in a region where the temperature varies between (77-85) ºF.

Another thing, how can I force the pcm to ignore the IAT at all???

[hquick]

Have a look at B4901 and B4902

[mr.prick]

Have a look at B4901 and B4902

these 2 tables are used when {B0109} is enabled.

are you the guy that was trying to "trick" the ECU by giving it a set IAT?
high/low IATs have a huge affect on your engine,
there is really no way around it.
i assume this is why we have LTFTs and STFTs.
try relocating the IAT sensor, maybe that will help some.

[odd boy]

thanks to you guys.

[redhardsupra]

i've seen situations where IAT sensor (the hardware) failed, and it just reported constant -40C, which is hugely off for most situations, so your temperature will be misreported, and all temp based modifers will throw off the tune, so spark, airmass, and all other things are gonna go heywire. you dont wanna deal with that.

[eurospec1]

I actually ran into this problem in my C5, that is already run in OLSD.

I was driving home one night, and 35 miles from home when the car started running terrible, i was data logging at the time and saw the IAT reading -40. I just re-did my VE table and everything was fine again, i actually drove the car for quite a while before getting around to fixing it (was a broken wire) with no negative affects.

[rally1]

If you unplug the IAT it will normally run very rich casuing the fuel trims to go a long way into the negitive.

[redhardsupra]

yea, fake cold temps are gonna make airmass go up, thus the computer will dump more fuel than necessary in reality.

[Sid447]

i've seen situations where IAT sensor (the hardware) failed, and it just reported constant -40C, which is hugely off for most situations, so your temperature will be misreported, and all temp based modifers will throw off the tune, so spark, airmass, and all other things are gonna go heywire. you dont wanna deal with that.

I've seen a locally "modified" car (Lumina SS) here which had the IAT sensor located behind the headlight and disconnected from the maf-pipe.
When scanned the IAT reading was steady at -40C and the car was running seriously rich.

[odd boy]

Welcome,

How is EFIlive tuning in UAE?? I am happy to see more people in the Middle East using this great device. "Big welcome from KSA"

Well, let's start with understanding the contribution of IAT in all tables;

1. {B4901} charge temperature blending

The PCM calculates the charge temperature (in degrees Kelvin) using the following formula 273.15+IAT+((ECT-IAT)*factor) where factor is obtained from this calibration, which will be used later in the VE calculations (g/cyl = VE*MAP/charge temperature)

This will be valid if {B0109} is set to yes.

2. {B4902} Charge Temperature Filter

Determines the rate of change of the calculated charge temperature in response to changes in the IAT or the ECT.

3. {B5911} Spark IAT table : Provides intake air temperature correction to spark timing.

4. {B5943} Spark IAT vs RPM Multiplier

This table contains the multiplier values for table {B5911} "Spark IAT Table" based on engine speed. Any value in table {B5911} "Spark IAT Table" will be multiplied by this amount before being summed in the final spark advance calculation.

* EXAMPLES *
0.0 = No Correction applied from IAT spark table.
1.0 = Use the full value defined in IAT spark table.
0.5 = Use 50% of the value defined in IAT spark table.

5. {B5944} Spark IAT vs ETC Multiplier

This table contains the multiplier values for table {B5911} "Spark IAT Table".
Any value in table {B5911} "Spark IAT Table" will be multiplied by this amount before being summed in the final spark advance calculation.
This table can be used to turn off IAT spark correction when the engine is cold (or hot).

So if we assume that the ECT is 80 C and IAT is 30 C, the correction temperature will be 273.15+IAT+((ECT-IAT)*factor )==> 273.15+30+((80-30)*.6) = 347.15 K.

Now will assume that the IAT is -40 C, the new value will be 375.15 K.

Then will put each value in the VE equation with assuming that VE=80, MAP= 35

1. When IAT = 30 C, corrected temp = 347.15 K :

g/cyl = VE*MAP/charge temperature ==> g/cyl = 80*35/347.15 = 8.06

2. When IAT = -40 C, corrected temp = 375.15 K :

g/cyl = VE*MAP/charge temperature ==> g/cyl = 80*35/375.15 = 7.46

From that, do you think the car will run richer or leaner if the IAT is -40 C???